Internal combustion engines are energy transforming mechanisms used by most automotive vehicles, and comprise basically two main parts: one or more engine heads and an engine block. At the bottom of the head (s) are located the combustion chambers (on Diesel engines, the combustion chambers are generally in the piston heads) and on the engine block are located the cylinders and the crankshaft assembly. The crankshaft assembly is composed by pistons, rods and crankshaft.
An engine converts the energy produced by combustion of the (fuel and air) mixture in the combustion chambers into mechanical energy capable of imparting movement to the wheels.
Since the driving power required for moving the automobile comes from the burning of the air/fuel mixture in the combustion chamber, and in order to ensure a homogeneous combustion, without burning oil, and still to prevent excessive passage of gases from the cylinder to the crank-case, it is necessary to use rings for promoting good sealing of the clearance existing between the piston and the cylinder wall.
Most of modern internal combustion engines that work according to the Otto and Diesel cycles use three rings, two of which being compression rings and one being an oil control (scraper) ring. The compression rings have the function of preventing passage of combustion gases into the crank-case, and the oil ring has the function of scraping excess oil from the cylinder wall and returning it to the crankcase, controlling the thickness of the oil film, so that the operation of the engine will take place within the premises of design and operation.
Another important function of the rings is that of serving as a bridge for transmitting heat from the piston to the cylinder wall/liner, where dissipation of the calorie takes place through the cooling system.
The oil scraping rings may be composed of one, two or three parts.
Two-piece or three-piece oil scraping rings are employed in the vast majority of applications, by virtue of their good global performance.
A two-piece ring comprises an annular body provided with two trapezoidal annular protrusions that face the cylinder sleeve and an equally annular, internal and concentric expanding element.
A three-piece ring, in turn, usually has a first upper annular segment and a second lower annular segment, which are associated to an intermediate expanding element, which presses in a controlled manner the upper and lower segments against the cylinder wall. The force exerted by the expanding element, which is nothing else than a resilient element, is calculated so that the oil film on the cylinder wall will have the desired thickness.
A single-piece ring, in turn, has a more restricted application due to the fact of having much flexibility inherent in its design, which, on the one hand, imparts excellent conformability to the ring when in operation, adjusting easily, and on the other hand makes its surface finish more difficult, which requires the ring to apply a great tangential force against the cylinder wall in order to guarantee that it will end up conforming to the cylinder sleeve during the engine run-in.
This high tangential force causes a high consumption of fuel by the engine, and still higher during the run-in operation, which renders the single-piece-ring solution widely left aside with respect to the two-piece or three-piece equivalents.
Until now, nobody had developed a single-piece oil-scraping ring capable of conforming easily to the cylinder by virtue of its flexibility and, concomitantly, applying a low tangential force, even during engine run-in, guaranteeing the correct oil-film thickness and decreasing the consumption of fuel by the engine, as well as emission of CO2.